1. The Field of the Invention
This invention relates to a device consisting of a modified intramedullary nail that contains the means for delivery of therapeutic and/or diagnostic agents directly to the fracture site.
2. The Relevant Technology
Intramedullary nails are used by orthopedic surgeons to stabilize long bone fractures. Bones typically involved would include femur, radius, ulna, humerus, fibula and tibia. The concept of intramedullary stabilization consists of mechanical reaming of the medullary canal, insertion of a form-fitting, rigid implant into the canal space and mechanically affixing the implant through insertion of screws or pins that travel through both the bone and the intramedullary device. Many variations of the intramedullary nail have been developed to address issues of strength, flexibility, ease of insertion and conformity to anatomical form. Some of the patented intramedullary nail apparatuses which deal with these mechanical concerns include U.S. Pat. No. 6,033,407 by Behrens, U.S. Pat. No. 5,814,047 by Emiho, U.S. Pat. No. 5,112,333 by Fixel, U.S. Pat. No. 5,100,404 by Hayes, U.S. Pat. No. 5,034,013 by Kyle, U.S. Pat. No. 4,976,714 by Aghion, U.S. Pat. No. 5,779,705 by Matthews, and U.S. Pat. No. 5,658,287 by Hofinann.
Beyond the mechanical requirements for stabilization of long bone fractures, many issues relating to the biochemistry of bone healing are of great significance for determining the outcome of medical intervention. To this end, many devices and materials have been designed to facilitate the delivery of therapeutic agents to the traumatized area. One of the earliest means for controlled introduction of therapeutic agents into a patient is through catheter delivery. Catheter delivery of agents is typically systemic due to the direct introduction of said agents into the patient""s bloodstream.
Several works more directly target bones with catheter systems. U.S. Pat. No. 5,203,770 by Wigness reveals a catheter system that travels through bones for better access to internal joint surfaces. Delivery of therapeutic agents directly to a joint surface is thought to facilitate a therapy for arthritic conditions. U.S. Pat. No. 4,772,261 by Von Hoff reveals a catheter system that delivers therapeutic agents into the intramedullary canal of non-traumatic bones, via a bone tap, which then functions as a semi-continuous drug-releasing reservoir for the entire body.
An alternative method for continuous delivery of therapeutic agents involves the bioerosion of an implantable material which releases into solution a variety of therapeutic substances. Polymer and polymer/ceramic composite materials are most often utilized as the matrix material. They both show good biocompatibility and are readily eroded in a physiological environment. A significant problem with these systems is that they both lack the mechanical strength to safely stabilize long bone fractures. Polymeric matrix systems for the delivery of a host of therapeutics via bioerosion include U.S. Pat. No. 5,855,915 by Pinkus, U.S. Pat. No. 5,629,009 and U.S. Pat. No. 5,545,409 by Laurencin, U.S. Pat. No. 5,607,474 by Athanasiou, U.S. Pat. No. 5,268,178 by Calhoun, U.S. Pat. No. 4,946,929 by D""Amore, U.S. Pat. No. 4,347,234 by Wahlig and U.S. Pat. No. 4,563,489 by Urist. Examples of ceramic-based bioerosion delivery systems would include U.S. Pat. No. 5,849,331 by Ducheyne, U.S. Pat. No. 4,218,255 by Bajpai and U.S. Pat. No. 5,972,384 by Thut.
The idea of merging the needed mechanical stabilization of a metallic intramedullary nail with therapeutic drug delivery has been conceived by several inventors. U.S. Pat. No. 5,618,286 by Brinker reveals an intramedullary fixation implant that includes solid antibiotic material packed along grooves in the implant. Significant drawbacks with this design include the inability to modify drug dosage or type once inserted and the inability to specifically target the fracture site for drug delivery. This design also does not allow for mechanical stabilization to be obtained, followed by an interval of no intraosseous therapeutic intervention prior to the possible initiation of pharmacological therapy. This would be beneficial because the potential for unassisted healing could be assessed, with the option of subsequent therapeutic intervention remaining available. U.S. Pat. No. 4,919,666 by Buchhorn reveals a design very similar to U.S. Pat No. 5,618,286 with the addition of a porous covering over the bioeroding agent to prevent bone growth into the grooves of the implant. As with the previous design, drawbacks with this design include the inability to modify drug dosage, regimen or type once inserted and the inability to specifically target the fracture site for drug delivery. U.S. Pat. No. 5,702,446 by Schenek reveals a hip stem prosthesis with internal channels that allows irrigation of an endosteal bone/prosthesis mesh surface via external injection of therapeutic fluids through a connected catheter tube. While this design would allow for modification of the drug profile, the delivery of the drug is not specific to a fracture site and the device provides no mechanism for fracture fixation. U.S. Pat. No. 5,836,949 by Campbell reveals a totally bioresorbable intramedullary nail. The nail is proposed to provide stabilization during the early stages of bone repair and effectively disappear over an extended period of time therefore eliminating issues associated with post-utility implant presence. Short-comings with this design include reduced mechanical strength compared to metallic nail systems and no delivery of therapeutic agents.
The proposed device is an intramedullary nail that functions as both a fracture stabilization device and as a means for delivery of therapeutic and/or diagnostic agents from the intramedullary position to the entire fracture surface. The catheter-based, drug delivery method uniquely provides maximum control over the type, rate and concentration of drug delivered and the ability to deliver the drug to the precise location of bone trauma.
The proposed intramedullary catheter nail is unique in the field of orthopedic surgery. It offers the surgeon a convenient method for obtaining fracture stabilization with the additional benefit of targeted, therapeutic drug delivery. The objects and advantages of the intramedullary catheter nail system are as follows.
1. Stabilization of long bone fractures equivalent to traditional intramedullary nails.
2. Precision delivery of various therapeutic agents from the intramedullary position to the entire fracture surface.
3. Controlled slow dosing of therapeutic agents allowing for constant maintenance of physiologically responsive drug concentrations at the fracture site.
4. Delivery of various drug classes such as growth factors, analgesics, chemotherapeutic, antibiotics, anti-inflammatories, diagnostics or mixtures of various components of differing classes to the fracture site.
5. Unlike bioerodible drug delivery, the intramedullary catheter nail allows for rapid alteration of the drug protocol to better adjust for individual patient responses.
6. Unlike bioerodible drug delivery, the intramedullary catheter nail allows for tailored sequences of drugs to be introduced to the fracture surface.
7. Unlike bioerodible drug delivery, the intramedullary catheter nail allows for periods of no drug delivery such that unassisted bone healing may be observed and evaluated.